1. Field of the Invention
This invention relates to a steering wheel for use in automobiles and other vehicles. More particularly, this invention relates to a steering wheel using fiber reinforced plastic (FRP) consisting of continuously long fibers as its reinforcing member.
2. Description of the Prior Art
Recent trends of automotive vehicles toward general reduction of weight has been encouraging use of increasing amounts of resins in automobile parts. Steering wheels are no exception. Resins of polyurethane, polypropylene, and other similar types have been adopted as materials for steering wheels. Since these resins have low strength, however, they have been invariably required to incorporate metallic reinforcement. Generally, round bars and pipes of iron are used as the metallic reinforcement. The weight of metallic reinforcement normally accounts for as much as about 40% of the entire weight of the steering wheel. The use of the metallic reinforcement, therefore, contradicts the inclination toward reduction of weight and proves disadvantageous.
FIG. 7 illustrates a typical conventional reinforcement of a steering wheel formed of round bars and round pipes. This reinforcement includes a core around which resins are molded for forming a steering wheel. The reinforcement of this steering wheel comprises reinforcing members 10, 11, and 12 respectively positioned in the corresponding parts of a ring, a sub-ring, and spokes of a steering wheel (hereinafter called as a ring part, a sub-ring part and spoke parts respectively). The reinforcing members 12 of the spoke parts and the reinforcing member 11 of the sub-ring part are formed of round bars ofiron. These reinforcing members 11, 12 are integrally bound by being welded at the outer edges of the reinforcing members 12. The inner ends of the reinforcing members 12 are fastened by welding to a boss plate 13a of iron plate supporting a boss 13 thereon.
The reinforcing member 10 of the ring part is formed of a pipe. Into the opposite ends of the reinforcing member 10 so formed of a pipe, the bent outer ends of the reinforcing members 12 of the spoke parts are inserted. The reinforcing member 10 and the reinforcing members 12 are joined by being welded where the latter are inserted into the former.
In the conventional reinforcement of a steering wheel illustrated in FIG. 7, the reinforcing member 10 of the ring part is formed of a pipe for the purpose of weight reduction. Since this pipe is made of iron, the overall weight is about 0.8 kg in the steering wheel of an ordinary automobile. This reinforcing member is rather heavy.
Since these reinforcing members 10, 11, and 12 are formed of round bars or round pipes of iron, the joints of these reinforcing members 10, 11, and 12 are inevitably welded one by one. Thus, the conventional reinforcement of a steering wheel has also proved disadvantageous from the standpoint of manufacture.
In addition, to permit this welding, the portions of the reinforcing members to be welded are not allowed to have a small wall thickness. the boss plate 13a as used generally at present has a wall thickness of about 2 mm. This fact constitutes one of the factors for the increase of weight.
The reduction of weight of the steering wheel brings about a desirable effect upon the prevention of vibrations which are transmitted through the steering system to the automobile driver during the travel of the automobile. Specifically, the magnitude of such vibrations is decreased in proportion as the weight of steering wheel is reduced. Thus, a further reduction of the weight of the steering wheel is still in demand.
Further recently, as described in the British Patent Publication No. 2004835A, a long fiber reinforced plastic formed of continuous beam, which are formed of a continuously long fiber strand of carbon fiber or glass fiber impregnated with resin such as epoxy resin, has been developed and known to be used in the formation of some lattice structures, where such a fiber reinforced plastic is wound onto a frame work forming a structure of a shape.
However, there has been a drawback in this engineering that, if there is contained in the structure any T-letter or Y-letter figured branch, the binding strength of the branch may not be strong enough to prevent the strands being released or broken by some outer force. Accordingly since the reinforcement of a steering wheel in this invention of the present appliction, which is intended to apply such a structure as described above, has a T-letter branch, there arises a similar drawback to the one of British Pat. No. 2004835A.